It is well known in the art to provide a four-stroke cycle internal combustion engine with a main combustion chamber in which air or a lean air-fuel mixture is provided and an auxiliary combustion chamber or prechamber connected with the main chamber by a restricted passage or orifice and in which a preferably rich air-fuel mixture is provided for ignition by a spark plug. In such engines the combustion originating in the prechamber forces into the main chamber a jet of burning gases, including unburned and partially burned mixture and combustion products. The burning jet, because of its high energy, is able to ignite a lean mixture in the main chamber, thereby permitting the burning of overall leaner mixtures in an engine than would be possible without the jet ignition process. Two examples of engines utilizing some of the many variations of the above-described principle are shown in U.S. Pat. Nos. 1,568,638 and 1,833,445 Summers.
In the main, the prechamber jet ignition principale has been applied to four-cycle spark ignition engines, and principle is thought there would be advantages in providing simple arrangements applicable to two-cycle engines in which inlet air or air-fuel mixture is admitted through piston controlled ports, rather than the poppet valves generally utilized in four-cycle engines.